ES2342091T3 - TRAINING OF SOLAR CELLS ON SUBSTRATES OF METAL SHEET. - Google Patents

Abstract

A method for forming an absorber layer of a photovoltaic device comprises forming a nascent absorber layer on a metal foil substrate; and using a roll-to-roll system to transport the substrate through a furnace. The nascent absorber layer and/or substrate is heated in the furnace and in an H 2 Se gas, H 2 S gas, or group VIA vapor without destroying the aluminum foil substrate.

Description

Formation of solar cells on substrates of metal foil

Field of the Invention

The present invention relates to the manufacture of photovoltaic devices, and more specifically when processing and annealing absorbent layers for devices photovoltaic

Background of the invention

Efficient photovoltaic devices, such like solar cells, they have been manufactured using layers absorbents made with alloys containing elements of the IB, IIIA and VIA groups, for example, copper alloys with indium and / or gallium or aluminum, and selenium and / or sulfur. Often these layers absorbents are called CIGS layers and devices resulting are often referred to as CIGS solar cells. The layer CIGS may be deposited on a substrate. It would be desirable manufacture a similar absorbent layer on a sheet substrate aluminum metal, because the aluminum metal sheet is relatively economical, light and flexible. Unfortunately the Current techniques for depositing CIGS absorbent layers are incompatible with the use of aluminum foil as a substrate

Typical deposition techniques include evaporation, cathodic deposition, chemical deposition in phase of steam and the like. These deposition processes are carried out typically at elevated temperatures and for prolonged periods. Both factors can result in damage to the substrate over which the deposition is occurring. Such damages can generated directly from changes in the material of substrate after exposure to heat, and / or from reactions undesirable chemicals driven by the heat of the process deposition Therefore, materials are typically required. Very robust substrate for the manufacture of CIGS solar cells. These limitations have excluded the use of aluminum and sheets  Metals based on aluminum foil.

An alternative deposition approach is the Solution-based printing of CIGS precussor materials on a substrate. Examples of printing techniques based on solutions are described, for example, in the PCT Published Application WO 2002/084 708 and in the commonly granted U.S. patent. 2005-0 183 767. The advantages of this approach to deposition include both the deposition temperature relatively less like the speed of the deposition process. Both advantages serve to minimize the potential for heat-induced damage, in the substrate on which the deposition is forming.

While deposition in solution is a stage to relatively low temperatures in cell manufacturing Solar CIGS, is not the only stage. In addition to deposition, a key stage in the manufacture of solar cells CIGS is the selenization and annealing of the CIGS absorbent layer. The selenization introduces selenium into the absorbent layer of CIG or CI to bulk, where the element is incorporated into the structure, while annealing provides the absorbent layer with the structure appropriate crystalline In the prior art, selenization and Annealing have been carried out by heating the substrate in the presence of H 2 Se or Se vapor, and maintaining this absorbent layer incipient at elevated temperatures for prolonged periods of weather.

While it would be desirable to use Al as substrate for solar cell devices due to both cost reduced as to the light nature of said substrate, the techniques Conventionals that effectively coat the CIGS absorbent layer they also heat the substrate at elevated temperatures, which has  As a result damage to Al substrates. There are several factors which result in degradation of the Al substrate after prolonged exposure to heat and / or compounds containing Selenium for prolonged periods. First, after the Prolonged heating, discrete layers inside a Al substrate coated with Mo can melt and form a intermetallic rear contact for the device, which decreases the expected electrical functionality of the Mo layer. In second instead, the interfacial morphology of the Mo layer is altered during heating, which may adversely affect the subsequent CIGS grain growth through changes in the patterns of nucleation that may arise on the surface of the Mo layer. Third, after extended warming, Al can emigrate towards the CIGS absorbent layer, deteriorating the function of the semiconductor. Fourth, the impurities that are present typically in the metal sheet of Al (for example Si, Fe, Mn, Ti, Zn and V) can move along with the mobile that is broadcast towards the solar cell after prolonged heating, which can impair the electronic and optoelectronic functions of the cell. Fifth, when Se is exposed to Al during relatively long periods and at relatively hot temperatures elevated, aluminum selenide can be formed, which is unstable. In moist air, aluminum selenide can react with water vapor to form aluminum oxide and hydrogen selenide Hydrogen selenide is a gas extremely toxic, whose free formation can represent a Security risk For all these reasons, the deposition to high temperatures, annealing and selenization are therefore both unfeasible for substances made of aluminum or aluminum alloys

Due to the long deposition stages duration at elevated temperature, and annealing, solar cells CIGS cannot be efficiently manufactured on substrates of aluminum (for example, flexible metal sheets composed of Al and / or Al) based alloys, and instead must be manufactured of heavier substrates made of more robust materials (and more expensive) such as stainless steel, titanium metal sheets or molybdenum, glass substrates, or metal coated glass or With metal oxides. In this way, even though the cells CIGS solar based on aluminum foil would be more Light, flexible and economical than steel sheet metal stainless, titanium or molybdenum, which glass substrates, or that glass substrates coated with metal or oxides metallic, current practice does not allow the metal sheet of Aluminum be used as a substrate.

WO03 / 007 386 discloses a photovoltaic device, comprising: a sheet substrate electrically conductive aluminum metal; at least one electrically conductive base electrode layer comprising a molybdenum layer; an adhesion layer located between the substrate of aluminum foil and electrode layer, said layer of adhesion comprising chromium; and an absorbent layer containing one  or more elements of the IB, IIIA and VIA groups arranged in the Aluminum foil substrate.

Summary

It is an objective of the present invention to give know an improved manufacturing process to protect the Aluminum substrate during manufacturing.

The present invention discloses a method improved formation of an absorbent layer of a device photovoltaic, according to claim 1. In the dependent claims other embodiments are set forth advantageous

Brief description of the drawings

The descriptions of the present invention can be easily understood considering the following description  detailed together with the attached drawings, in which:

Figure 1 is a schematic diagram in cross section, illustrating the manufacture of a layer absorbent according to an embodiment of the present invention.

Description of specific embodiments

Although the following detailed description It contains many specific details for illustrative reasons, any subject matter expert will appreciate that many variations and alterations to the following details are within the scope of the invention. Therefore, exemplary embodiments of the invention described below, are exposed without any loss of generality for the claimed and unimposed invention limitations to it.

The embodiments of the present invention allow the manufacture of CIGS absorbent layers on substrates Aluminum foil. According to realizations of the present invention, an incipient absorbent layer containing elements of groups ID and IIIA formed on a substrate of aluminum by deposition in solution, can be annealed by rapid heating from room temperature to a plateau temperatures range between about 200ºC and about 600ºC. The temperature remains in the plateau range for about 2 minutes and about 30 minutes, and then it comes down. Alternatively, in an example that is not part of the invention, the annealing temperature could be modulated to oscillate in the inside a temperature range without staying in a concrete plateau temperature.

Figure 1 describes a photovoltaic device 100 partially manufactured, and a rapid heating unit 110; the device generally includes a sheet substrate 102 Aluminum metal, an optional 104 base electrode, and a layer incipient absorbent 106. The metal sheet substrate 102 of aluminum can be from about 5 microns to about one hundred or more microns from thickness, and of any suitable width and length. The substrate 102 aluminum foil can be made of aluminum or of an aluminum based alloy. Alternatively, the substrate 102 aluminum foil can be manufactured by metallization of a polymeric metal sheet substrate where the polymer is selected from the group of polyesters, naphthalate polyethylene, polyetherimides, polyethersulfones, polyether ether ketone, polyimides and / or combinations of the above. By way of example, the substrate 102 may be in the form of a long sheet of Aluminum foil suitable for processing in a roll to roll system. The base electrode 104 is made of a conductive material electrically compatible with the processing of the incipient absorbent layer 106. By way of example, the electrode base 104 may be a molybdenum layer, for example, of approximately 0.1 to 25 microns thick, and more preferably from about 0.1 to 5 microns thick. Base electrode layer it can be deposited by cathodic deposition or evaporation, or alternatively by chemical vapor deposition (CVD, chemical vapor deposition), atomic layer deposition (ALD, atomic layer deposition), sol-gel coating, electroplasty and the like.

Aluminum and molybdenum can inter-diffuse in each other, with effects harmful electronic and / or optoelectronic devices in the device 100. To inhibit such inter-diffusion, you can an intermediate interfacial layer 103 being incorporated between the substrate 102 of aluminum foil and base electrode 104 Molybdenum The interfacial layer may be formed of compounds such as nitrides (which include tantalum nitride, nitride tungsten and silicon nitride) oxides and / or carbides. The thickness of this layer may vary from 10 nm to 50 nm, and more preferably from 10 nm to 30 nm.

The incipient absorbent layer 106 includes material containing elements of groups 1B, IIIA and (optionally) VIA. Preferably, the copper (Cu) of the layer absorbent is the element of group IB, gallium (Ga) and / or indium (In) and / or aluminum may be the elements of group IIIA, and selenium (Se) and / or sulfur (S) elements of the VIA group. The group element VIA can be incorporated into the incipient absorbent layer 106 when initially deposited in solution or during processing subsequent to form a final absorbent layer from the incipient absorbent layer 106. The incipient absorbent layer 106 It can be about 1000 nm thick when deposited. He subsequent rapid thermal process and the incorporation of elements of the VIA group can change the morphology of the absorbent layer resulting, so that it increases its thickness (for example, as much up to about twice the thickness of the layer incipient under certain circumstances).

The manufacture of the absorbent layer in the aluminum sheet metal substrate 102 is relatively direct. First, the incipient absorbent layer is deposited on the substrate 102 directly on the aluminum or on a higher layer such as electrode 104. By way of example, and without loss of generality, the incipient absorbent layer is deposited as a film of a precursor material based on solution, which contains nanoparticles that include one or more elements of groups IB, IIIA and (optionally) VIA. Be describe examples of said films in said techniques of solution-based printing, for example in the granted patent commonly U.S. 2005-0 183 767, titled "SOLUTION-BASED FABRICATION OF PHOTOVOLTAIC CELL "(manufacturing based on photovoltaic cell solution) and also in PCT Publication WO 02/084 708 entitled "METHOD OF FORMING SEMICONDUCTOR COMPOUND FILM FOR FABRICATION OF ELECTRONIC DEVICE AND FILM PRODUCED BY SAME "(method of forming a semiconductor composite film for the manufacture of electronic device and film produced by it).

Alternatively, but not included in the invention, the incipient absorbent layer 106 may be manufactured by a sequence of atomic layer deposition reactions or by any other process normally used to form said layers. Atomic layer deposition of absorbent layers IB-IIIA-VIA is described, for example, in the document commonly granted, US 2005-0 186 342, entitled "FORMATION OF CIGS ABSORBER LAYER MATERIALS USING ATOMIC LAYER DEPOSITION AND HIGH THROUGHPUT SURFACE TREATMENT ON COILED FLEXIBLE SUBSTRATES "(formation of CIGS absorbent layer materials using atomic layer deposition and high performance surface treatment on flexible spiral substrates).

Next, the incipient absorbent layer 106 is annealed by instantaneous heating, and / or the substrate 102, from an ambient temperature to a temperature range of average plateau between about 200ºC and about 600ºC, with the unit of heating 110. Heating unit 110 provides preferably enough heat to rapidly increase the temperature of the incipient absorbent layer 106 and / or the substrate 102 (or a significant part thereof) for example, between about 5ºC / s and about 150ºC / s. As an example, the unit of heating 110 may include one or more infrared lamps (IR) that provide sufficient radiant heat. As an example, 8 IR lamps at a nominal power of about 500 W located each approximately to between 3.1750 mm (1/8 '') and 24.4 mm (1 '') from the surface of the substrate 102 (4 above and 4 below the substrate, all directed towards the substrate) can provide heat radiant enough to process a substrate area of about 25 cm2 per hour, in a tube oven of about 101.6000 mm (4``). The lamps can be activated gradually in a controlled manner, by example at a rising speed of about 10 ° C / s. The experts in the subject may conceive other types of font configurations of heat that can be used as heating unit 110. For example, in the roll-to-roll manufacturing line, the heating and other processes can be carried out by use of IR lamps separated by 25.4 mm (1``) along the length of the processing region, with IR lamps located homogeneously both above and below the substrate, and where both IR lamps both above and below the substrate are directed towards the substrate. Alternatively, IR lamps they could be placed only above or only below the substrate 102, and / or in configurations that increase lateral warming from the side of the chamber towards the side of the substrate 102.

The absorbent layer 106 and / or the substrate at 102 is maintained in the average plateau temperature range for between about 2 minutes and about 30 minutes. For example, the temperature can be maintained in the desired range by reducing the amount of heat from heating unit 110 to a level suitable. In the example of IR lamps, heat can be reduced simply by disconnecting the lamps. Alternatively, The lamps can be actively cooled. The temperature of the absorbent layer 106 and / or substrate 102 is reduced subsequently to an appropriate level, for example, by continue to reduce or disconnect the heat supply from of the heating unit 110.

In embodiments of the invention, they are carried sequentially perform two or more discrete annealing stages or continuous, in which elements of the VIA group are incorporated such as selenium or sulfur, in a second or last stage. For example, the incipient absorbent layer 106 may be exposed to H2 Se gas, H2S gas or Se vapor before, or during, the instant heating or rapid thermal processing (RTP, rapid thermal processing). In this embodiment, the relative brevity of exposure allows the aluminum substrate to resist better the presence of gases and vapors, especially at thermal levels high.

Once the incipient absorbent layer 106 has been annealed, additional layers can be formed to complete the device 100. For example, a layer is typically used in window as a couple for the absorbent layer. By way of example, the binding partner layer may include cadmium sulfide (CdS), zinc sulphide (ZnS) or zinc selenide (ZnSe) or some combination of two or more of these. Layers of these materials, for example by chemical bath deposition, surface chemical deposition, or aerosol pyrolysis, up to a thickness between 50 m and 100 nm. In addition, a transparent electrode, for example a layer of conductive oxide, in the window layer by cathodic deposition, deposition of steam, CVD, ALD, electrochemical atomic layer epitaxy and Similar.

The embodiments of the present invention overcome the disadvantages associated with the prior art by fast thermal processing of CIGS absorbent layers incipients deposited, or otherwise formed, on substrates of aluminum. Aluminum substrates are much cheaper and lighter than conventional substrates. Therefore, the solar cells based on aluminum substrates can have a lower cost per watt and one more energy return period short, compared to conventional solar cells based on silicon. In addition, aluminum substrates allow a flexible form factor that allows both a roll impression to high performance roll during cell manufacturing solar, as faster and easier installation processes during the installation of modules and solar systems.

The embodiments of the present invention allow the manufacture of light photovoltaic devices and Economical on aluminum substrates. The processing of instantaneous heating / rapid thermal processing of the layer incipient absorbent 106, allows proper annealing and incorporation of elements of the VIA group without damaging or destroying the substrate 102 of aluminum foil. The range of plateau temperatures is sufficiently below the point of fusion of aluminum (about 660ºC) to avoid damage or destroy the aluminum foil substrate. The utilization of aluminum foil substrates greatly reduces material costs of photovoltaic devices, for example, solar cells, manufactured on said substrates, reducing that way the cost per watt. Economies of scale can be obtained processing the aluminum foil substrate from roll to roll form, building the various layers of photovoltaic devices on the substrate as it passes through a series of stages of deposition, annealing and other process stages.

While the above is a complete description of the preferred embodiment of the present invention, it is possible Use various alternatives, modifications and equivalents. For the therefore, the scope of the present invention should not be determined referencing the above description if not doing reference to the appended claims, with the full scope of its equivalents

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References cited in the description

The list of references cited by the applicant is for the convenience of the reader only. It is not part of the European Patent document. Although special care has been taken in collecting references, errors or omissions cannot be ruled out and the EPO disclaims all responsibility in this regard .

Patent documents cited in the description

WO 2002 084 708 A [0004]

US 2005 0 183 767 A [0004] [0017]

WO 03 007 386 A [0008]

WO 02 084 708 A [0017]

US 2005 0 186 342 A [0019]

Claims (8)

1. Method for forming an absorbent layer of a photovoltaic device, comprising the steps of:

provide a substrate comprising at least one metal sheet substrate electrically conductive aluminum (102), at least one layer interface (103) that includes at least one selected material between the group consisting of a carbide, an oxide, a nitride, tantalum nitride, tungsten nitride and silicon nitride, and at least one electrically based electrode layer (104) conductive comprising a molybdenum layer, in which the layer interface is located between the metal sheet substrate of aluminum and the base electrode layer and in which the interface layer acts as a diffusion barrier to inhibit the inter-diffusion of molybdenum in the electrode and of aluminum in the substrate during heating, and,

forming an incipient absorbent layer (106) containing one or more elements of group IB, IIIA and VIA on the aluminum foil substrate, characterized by:

deposit the incipient absorbent layer from a solution of materials nanoparticle precursors;

anneal the layer incipient absorbent deposited and / or the substrate by:

to warm quickly the incipient absorbent layer and / or the substrate from a ambient temperature up to a plateau temperature range of between 200ºC and 600ºC, at a speed between 5ºC / s and 150 ° C / s;

keep the cape absorbent and / or substrate in the plateau temperature range for between 2 minutes and 30 minutes; Y

reduce the temperature of the absorbent layer and / or the substrate; and

incorporate one or more elements of the VIA group to the absorbent layer in a second or subsequent annealing stage.

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2. The method of claim 1, wherein said one or more elements of the VIA group include selenium. 3. The method of claim 1, wherein said one or more elements of the VIA group include sulfur. 4. The method of claim 1, wherein rapid heating of the incipient absorbent layer and / or the substrate is carried out by radiant heating of the incipient and / or substrate absorbent layer. 5. The method of claim 4, wherein one or more infrared lamps apply radiant heat. 6. The method of claim 1, wherein The formation and rapid heating stages of the absorbent layer  incipient take place when the substrate passes through the roll to roll process. 7. The method of claim 1, wherein The aluminum foil substrate has a thickness of at least 5 microns or more. 8. The method of claim 1, wherein said annealing stages are discrete or continuous.